Third generation mobile telecommunications systems aim at providing end-users, apart from terminal and personal mobility, with enhanced services. Compared to second generation systems, enhancements that will cover features all the way between the end-user and the core network elements are required, i.e. from mobile terminals to radio access and fixed networks. As an example, the Universal Mobile Telecommunications System (UMTS) is a third generation system which assumes a B-ISDN core network.
Significantly, utilization of existing technologies gives rise to numerous issues concerning the protocols employed. The most essential aspect requiring further investigation is how protocol specification effort can be minimized by re-using existing protocols and functionality while preserving the functional specifications and performance goals that UMTS is setting. The UMTS concept is being developed and will be integrated with the International Telecommunication Union (ITU) as a proposal for an IMT-2000 standard. UMTS/IMT-2000 will provide ubiquitous wireless access to next-generation personalized services wherever suitable frequencies are available. Global Systems for Mobile Communication (GSM) operators have several options for delivering enhanced services. For example, they may use GSM in the existing frequency spectrum to deliver UMTS/IMT-2000-capable services, they may use GSM and WCDMA (Wideband Code Division Multiple Access) in the existing spectrum or they may use GSM and WCDMA in the existing spectrum combined with WCDMA in a new 2 GHZ UMTS/IMT-2000 spectrum. All approaches offer low entry costs, a high degree of investment flexibility, since roll out can take place in line with market demand, as well as extensive reuse of existing GSM equipment. Not only does WCDMA offer full backwards compatibility with GSM, it fully draws on GSM as the core network, including well-proven GSM functionality.
FIG. 1 shows a diagram of network components of third generation (3G) mobile networks (UMTS, IMT-2000) and the corresponding interfaces used for connecting the network components. According to FIG. 1, a GSM network 10 is connected via an Ater interface to a third generation core network 7. The third generation core network 7 can be based on GSM technology, i.e. it may comprise a GSM mobile switching center (MSC). In this case, the same MSC can handle both GSM and 3G radio access networks via an open A interface.
A 3G radio access network (3G RAN) 2 is connected via an Iu interface (the interface between the radio network controller—RNC- and the core network as specified by the 3G standards) to the core network 7. Thus, in case a GSM MSC is used in the core network 7, the Iu interface must be adapted through an interworking unit (IWU) to the A interface of the GSM MSC. Furthermore, transcoders (TCs) (not shown) are located at the core network sides of the Ater interface and the ATM based Iu interface, wherein speech is transmitted in coded format over these interfaces. The TCs adapt the respective coding of the Ater interface and the Iu interface to the coding required for the open A interface of the core network 7. The TC arranged between the Iu interface and the A interface is a 3G TC and may be located in the IWU or may be part of the radio network controller (RNC) provided in the 3G RAN 2. In the latter case, an Iu interface is not provided. Another possibility is to provide a dedicated 3G MSC for the 3G RAN 2.
The core network 7 is connected via an ISUP (ISDN Signaling User Part) interface to a PSTN (Public Switched Telephone Network) and an ISDN (Integrated Services Digital Network). The ISUP interface provides the required ISDN call set up and control functions. Furthermore, the core network 7 is connected via a TCP/IP (Transmission Control Protocol/Internet Protocol) interface to the Internet.
Accordingly, the Internet, PSTN or ISDN can be accessed from the cellular GSM or 3G RAN networks 10 and 2 via the common core network 7 by means of a usual GSM mobile station (MS) 1a, a MS 1b having a GSM and a 3G capability, and a 3G MS 1c with enhanced third generation capabilities.
In addition to the above transcoding function, the core network 7 may comprise additional adaptation functions, for example modems and video codecs. However, similar to the TCs, these signal processing functions have to be separately provided at each access network interface, such that an increased number of network resources is required.
On the other hand, the interconnections to other networks currently require to offer real-time transport capabilities via IP (Internet Protocol) based interfaces. Therefore, interconnecting devices, typically called gateways (GW), are required, which further increase the number of network resources. Thus, a simple method for connecting mobile networks to IP based networks is required. Moreover, it would be beneficial to have an open interface between network controlling devices such as the MSC and actual user-plane processing functions.